Comparison of bitterness of caffeine and quinine by a time – intensity procedure

Temporal bitterness sequences elicited by four equi-bitter concentrations of caffeine and quinine were evaluated by a time – intensity procedure. For both compounds, the increase in bitterness intensity was highly correlated with an increased duration of aftertaste, although the time to maximum intensity did not change. For equi-bitter solutions, the duration of aftertaste was influenced by the specific tastant, and was longer for caffeine. Caffeine elicited a faster maximum rate of onset and slower maximum rate of decay of bitterness. Only one significant difference between subjects who were sensitive to l-phenyl-2-thiourca (PTC) and those who were non-tasters was found. Tasters rated the maximum intensity of quinine solutions higher than non-tasters.